Two major purposes of this study are to: 1) Characterize beta cell function and reserve in aging and type 2 (noninsulin dependent) diabetic subjects and, 2) To try to distinguish hyperglycemia in diabetes mellitus (DM) from that seen in the aging process. To distinguish the glucose intolerance of DM from that of aging is important because of the associated risk of complications in DM. A related purpose is to try to characterize type 2 DM into subtypes based on beta cell function and reserve. DM may be characterized by different genetic subtypes as well. Some emphasis will be placed on one autosomal dominant genetic subtype MOHY (maturity onset hyperglycemia of the young, MODY, Mason-type). The major tool will be urinary C-peptide which is a simple measure of integrated, prehepatic insulin production. It will be studied in conjunction with oral glucose tolerance tests, the hyperglycemic glucose clamp and euglycemic insulin clamp techniques, a mixed meal and a mixed meal following prednisone. (We have used the last two stimuli extensively in okther studies using urinary C-peptide and demonstrated their clinical utility.) Following this study in a limited number of subjects, a more extensive epidemiologic study will be undertaken with emphasis on beta cell function in aging and DM. Finally, to further characterize subtypes of type 2 DM, a search for genetic markers and abnormal insulins will be initiated. We have extensively studied urinary C-peptide as it related to body weight, dietary intake, and the effect of prednisone. It affords a new way of looking at beta cell function and because of its simplicity is particularly appealing in studies of aging subjects and its potential applicability to epidemiologic studies.